Casting of metal objects

Abstract

The mould assembly comprises mould segments of generally non-thermally conductive material which define a mould cavity for receiving liquid metal through at least one in-gate. A thermal extraction member of a high thermally conductive material contacts a portion of the mould cavity through which heat can be extracted rapidly to establish positive thermal gradients in the casting and thereby promote directional solidification. The mould assembly is also provided with a seal to selectively isolate the mould assembly from the liquid metal source to allow the mould assembly to be removed from the casting station to the cooling station before any substantial solidification has occurred, providing a more efficient use of the casting station.

We claim: 
     
       1. A mold assembly for the production of metal castings by solidification of molten metal, the mold assembly defining a mold cavity for receiving liquid metal and comprising: at least one mold segment formed from relatively low thermal conductivity material;   a primary inlet for filling said mold cavity with liquid metal;   a feeding system for feeding liquid metal to said mold cavity during solidification of metal in said mold cavity for compensating for shrinkage of metal during solidification; and   at least one thermal extraction member of a relatively high thermal conductivity material, said thermal extraction member defining part of said mold cavity and being positioned opposite said feeding system.   
     
     
       2. A mold assembly as recited in claim 1, wherein said mold cavity, said feeding system and said at least one thermal extraction member are shaped, sized and positioned relative to one another such that said mold assembly can be oriented such that when a liquid metal is solidifying in said mold cavity, said at least one thermal extraction member causes rapid and positive extraction of heat from said solidifying liquid metal to thereby establish and maintain positive thermal gradients within said solidifying liquid metal substantially for the duration of solidification of said solidifying liquid metal, whereby directional solidification in a direction from said thermal extraction member upward toward said feeding system is achieved throughout substantially all of the solidifying liquid metal. 
     
     
       3. A mold assembly as recited in claim 1, further comprising means for sealing said mold cavity. 
     
     
       4. A mold assembly as recited in claim 3, wherein said means for sealing said mold cavity comprises a sliding plate, an electromagnetic valve or means for freezing liquid metal. 
     
     
       5. A mold assembly as recited in claim 1, wherein said feeding system comprises a means for feeding liquid metal to said mold cavity during solidification of metal in said mold cavity for compensating for shrinkage of metal during solidification. 
     
     
       6. A mold assembly as recited in claim 1, wherein said at least one thermal extraction member is readily removable. 
     
     
       7. A mold assembly as recited in claim 1, wherein a portion of said at least one thermal extraction member is exposed to an environment outside said mold assembly. 
     
     
       8. A mold assembly as recited in claim 1, wherein said at least one mold segment is made of a relatively low thermal conductivity particulate material. 
     
     
       9. A mold assembly as recited in claim 1, wherein said primary inlet is proximate said at least one thermal extraction member. 
     
     
       10. A mold assembly as recited in claim 1, wherein said primary inlet fills via said feeding system. 
     
     
       11. A mold assembly for the production of metal castings by solidification of molten metal, the mold assembly defining a mold cavity for receiving liquid metal and comprising: at least one mold segment formed from relatively low thermal conductivity material;   a primary inlet for filling said mold cavity with liquid metal;   a feeding system for feeding liquid metal to said mold cavity during solidification of metal in said mold cavity for compensating for shrinkage of metal during solidification, said primary inlet filling via said feeding system; and   at least one thermal extraction member of a relatively high thermal conductivity material, said thermal extraction member defining part of said mold cavity and being positioned opposite said feeding system.   
     
     
       12. A mold assembly as recited in claim 11, wherein said mold cavity, said feeding system and said at least one thermal extraction member are shaped, sized and positioned relative to one another such that said mold assembly can be oriented such that when a liquid metal is solidifying in said mold cavity, said at least one thermal extraction member causes rapid and positive extraction of heat from said solidifying liquid metal to thereby establish and maintain positive thermal gradients within said solidifying liquid metal substantially for the duration of solidification of said solidifying liquid metal, whereby directional solidification in a direction from said thermal extraction member upward toward said feeding system is achieved throughout substantially all of the solidifying liquid metal. 
     
     
       13. A mold assembly as recited in claim 11, further comprising means for sealing said mold cavity. 
     
     
       14. A mold assembly as recited in claim 13, wherein said means for sealing said mold cavity comprises a sliding plate, an electromagnetic valve or means for freezing liquid metal. 
     
     
       15. A mold assembly as recited in claim 11, wherein said feeding system comprises a means for feeding liquid metal to said mold cavity during solidification of metal in said mold cavity for compensating for shrinkage of metal during solidification. 
     
     
       16. A mold assembly as recited in claim 11, wherein said at least one thermal extraction member is readily removable. 
     
     
       17. A mold assembly as recited in claim 11, wherein a portion of said at least one thermal extraction member is exposed to an environment outside said mold assembly. 
     
     
       18. A mold assembly as recited in claim 11, wherein said at least one mold segment is made of a relatively low thermal conductivity particulate material. 
     
     
       19. A mold assembly for the production of metal castings by solidification of molten metal, the mold assembly defining a mold cavity for receiving liquid metal and comprising: at least one mold segment formed from relatively low thermal conductivity material;   a primary inlet for filling said mold cavity with liquid metal;   a feeding system for feeding liquid metal to said mold cavity during solidification of metal in said mold cavity for compensating for shrinkage of metal during solidification; and   at least one thermal extraction member of a relatively high thermal conductivity material, said thermal extraction member defining part of said mold cavity and being positioned opposite said feeding system, said primary inlet being proximate said at least one thermal extraction member.   
     
     
       20. A mold assembly as recited in claim 19, wherein said mold cavity, said feeding system and said at least one thermal extraction member are shaped, sized and positioned relative to one another such that said mold assembly can be oriented such that when a liquid metal is solidifying in said mold cavity, said at least one thermal extraction member causes rapid and positive extraction of heat from said solidifying liquid metal to thereby establish and maintain positive thermal gradients within said solidifying liquid metal substantially for the duration of solidification of said solidifying liquid metal, whereby directional solidification in a directional from said thermal extraction member upward toward said feeding system is achieved throughout substantially all of the solidifying liquid metal. 
     
     
       21. A mold assembly as recited in claim 19, further comprising means for sealing said mold cavity. 
     
     
       22. A mold assembly as recited in claim 21, wherein said means for sealing said mold cavity comprises a sliding plate, an electromagnetic valve or means for freezing liquid metal. 
     
     
       23. A mold assembly as recited in claim 19, wherein said feeding system comprises a means for feeding liquid metal to said mold cavity during solidification of metal in said mold cavity for compensating for shrinkage of metal during solidification. 
     
     
       24. A mold assembly as recited in claim 19, wherein said at least one thermal extraction member is readily removable. 
     
     
       25. A mold assembly as recited in claim 19, wherein a portion of said at least one thermal extraction member is exposed to an environment outside said mold assembly. 
     
     
       26. A mold assembly as recited in claim 19, wherein said at least one mold segment is made of a relatively low thermal conductivity particulate material. 
     
     
       27. A mold assembly for the production of metal castings by solidification of molten metal, the mold assembly defining a mold cavity for receiving liquid metal and comprising: at least one mold segment formed from relatively low thermal conductivity material;   a feeding system for feeding liquid metal to said mold cavity during solidification of metal in said mold cavity for compensating for shrinkage or metal during solidification;   at least one thermal extraction member of a relatively high thermal conductivity material, said thermal extraction member defining part of said mold cavity and being positioned opposite said feeding system; and   means for sealing said mold cavity.   
     
     
       28. A mold assembly as recited in claim 27, wherein said mold cavity, said feeding system and said at least one thermal extraction member are shaped, sized and positioned relative to one another such that said mold assembly can be oriented such that when a liquid metal is solidifying in said mold cavity, said at least one thermal extraction member causes rapid and positive extraction of heat from said solidifying liquid metal to thereby establish and maintain positive thermal gradients within said solidifying liquid metal substantially for the duration of solidification of said solidifying liquid metal, whereby directional solidification in a direction from said thermal extraction member upward toward said feeding system is achieved throughout substantially all of the solidifying liquid metal. 
     
     
       29. A mold assembly as recited in claim 27, wherein said means for sealing said mold cavity comprises a sliding plate, an electromagnetic valve or means for freezing liquid metal. 
     
     
       30. A mold assembly as recited in claim 27, further comprising a primary inlet which fills via said feeding system. 
     
     
       31. A mold assembly as recited in claim 27, further comprising a primary inlet proximate said at least one thermal extraction member.